Well, on a serious note instead of inputting more silliness, like CastIron mentions, this is one of those things that simply has far too many variables to take into account to really be easily calculated.

The one endo i've done as a result of braking was as a kid, on my mountain bike with moderate quality indirect pull cantilever brakes (not exactly the pinnacle of stopping power). Normally, I wouldn't even consider these brakes potent enough to do such a thing, but they were apparently